What does the Bible say about adoption

Sonship - Bible lexicon

The Greek word is υίοθεσία and denotes the adoption of sons or the installation of persons in the position of sons, with all the advantages associated with it. Natural examples of this can be found in A. T. with Moses, who was a son adopted by Pharaoh's daughter (Ex. 2.10), and with Esther, who was adopted by her cousin Mordokai (Est 2.7).

In a higher sense, Israel was God's adopted son. Moses was commissioned to say to Pharaoh: "Thus says the Lord: My son, my firstborn, is Israel" (Ex. 4.22; cf. also Deut. 14.1; Is 43.6) Paul could say, when he enumerated the privileges of Israel, that the sonship belonged to them (Rom. 9.4) In a much higher sense, against the background of the finished work of redemption, those who believe in the Lord Jesus Christ are in the new Creation sons by the gift of sonship. The Spirit of the Son of God is given to them so that they may call God "Abba Father". They are not only sons, but they know and enjoy this relationship with all its blessed benefits (Gal 4: 5, 6). The Christian receives the spirit of sonship, whereby the Holy Spirit testifies with his spirit that he is a child of God. But he does not yet enter into the full blessing of the Son of God; for we who have the firstfruits of the Spirit groan within ourselves, waiting for sonship - the redemption of our body (Rom. 8: 15-23). All of this is certain for believers, for they are chosen in Christ Jesus and predestined "to be sonship through Jesus Christ for themselves, according to the pleasure of his will" (Eph 1: 4, 5).